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Source: LinuxExposed - Posted by Adam Chalemian
A network intruder will look for security weaknesses at every point in your network architecture. If you have adequately locked down the Physical, Data Link, Network, and Transport layers of your network, the wily hacker will simply move up to those . . .
A network intruder will look for security weaknesses at every point in your network architecture. If you have adequately locked down the Physical, Data Link, Network, and Transport layers of your network, the wily hacker will simply move up to those protocols and services your network does expose to the Internet. These application-specific protocols are actually much easier to exploit, so many hackers start there and drop down to the Network or Transport level when they need to circumvent a protocol's security mechanisms. In this article, we'll go over each of the most commonly used Internet services, briefly examining each for their weaknesses and abuse potential. First, however, we'll discuss sockets and services ingeneral, identifying typical service vulnerabilities so you can identify potential problems when you need to install services on your own network. In this article, we'll go over each of the most commonly used Internet services, briefly examining each for their weaknesses and abuse potential. First, however, we'll discuss sockets and services ingeneral, identifying typical service vulnerabilities so you can identify potential problems when you need to install services on your own network.
Which services are safe to allow through your firewall, which are not safe, and which ones do you do need to keep an eye on? When a new service becomes popular, or when you want to give your network clients a new Internet-based tool, what do you look for when you evaluate the service?
Complex services are easier to exploit than simple services. The Echo service, for example, simply transmits back to the client whatever the client sends to it. The Echo service is useful for debugging and for network connectivity testing, but it is difficult to see how the Echo service could be exploited to gain control of the computer running the service. Since the Echo service accepts data from theclient, however, it must be programmed to correctly handle being fed too much data at once.
